JP2004322630A - Phase change type information recording medium and sputtering target - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase change type information recording medium in which initial crystallization is easy, recording sensitivity is excellent at a high line speed with the same capacity as that of for DVD-ROM and with the recording line speed of ten times or more, overwrite recording can be executed, and which has excellent storage reliability. <P>SOLUTION: At least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer are formed on a transparent substrate in this order in the phase change type information recording medium. The recording of the information is executed by the reversible phase changes of a crystalline state and a noncrystalline state of the phase change recording layer by the irradiation with a laser beam. The alloy, which is the main component of a material constituting the phase change recording layer, has the composition formulas of Sn<SB>α</SB>Sb<SB>β</SB>Ga<SB>γ</SB>Ge<SB>δ</SB>[wherein α, β, γ, and δ satisfy α+β+γ+δ=100 and represent a composition ratio (atom%) of each element], and 5≤α≤25, 40≤β≤91, 2≤γ≤20, and 2≤δ≤20 are satisfied. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a phase-change information recording medium capable of recording and reproducing information by causing an optical change in a material constituting a recording layer by irradiating a laser beam, and rewritable, and a method for manufacturing the same. Of the sputtering target.

  At present, with regard to DVD-based recording layer materials, a system capable of 2.5-speed (about 8.5 m / s) speed recording has been developed, and the demand for high-speed recording is increasing. The phase change recording material used for DVD + RW is an improved version of the AgInSbTe-based high-speed recording material used for CD-RW, and enables recording and erasing up to a high linear velocity. In this material system, a material having a higher Sb content than that of a recording material compatible with CD-RW is used in order to correspond to the recording speed of a high linear velocity recording region. However, a material having a high Sb composition ratio is crystallized. Although the speed is increased, there is a problem that the crystallization temperature is lowered. It has been experimentally confirmed that a decrease in the crystallization temperature leads to deterioration in storage reliability. The problem of the storage reliability of the information recording medium has been suppressed to a level that does not pose a practical problem up to a DVD quadruple speed medium by increasing Ag in the recording material or adding a fifth element such as Ge. When the amount of Sb is increased to achieve high linear velocity recording, the crystallization temperature sharply drops, and the stability of the amorphous mark becomes extremely poor. From this, it is presumed that the practical use of a high-speed recording medium using the AgInSbTe system is limited to DVD quadruple speed.

A GaSb material is also being studied as a material for high-speed recording at 4 × speed or higher. The GaSb material system is capable of high-speed recording and at the same time has excellent storage reliability, but has a disadvantage in that the melting point is as high as 600 ° C., so that the recording sensitivity is low, and that high-speed recording requires high power. . In order to increase the speed of the GaSb system, it is necessary to increase the crystallization speed by increasing the amount of Sb. However, if the amount of Sb exceeds 90 atomic%, the phase of Sb is separated. A problem arises in that it becomes impossible to perform the formation uniformly. If the initial crystallization cannot be performed uniformly, the initial recording characteristics from the initial recording to about 10 repetitions will be significantly deteriorated, so that it cannot be put to practical use.
The AgInSbTe-based high-speed recording material is described in Patent Document 1, the GeGaSbTe-based material is described in Patent Document 2, the GeInSbTe-based material is described in Patent Document 3, and the InSbSn-based material is described in Patent Documents 4 and 5, respectively. .

JP-A-2000-339751 JP-A-2002-225437 JP-A-2002-264515 JP-A-9-286174 JP-A-9-286175

INDUSTRIAL APPLICABILITY The present invention facilitates initial crystallization, has good recording sensitivity even at the same linear capacity as DVD-ROM, and has a recording linear velocity of 10 times or more. Another object of the present invention is to provide an excellent phase change type information recording medium and a sputtering target for manufacturing the same.
When information is to be recorded on a recording medium by CAV (constant rotation speed method), a recording medium having excellent repetitive recording characteristics in a wide recording linear velocity region is required because the recording linear velocity differs depending on the radial position. Accordingly, an object of the present invention is to provide an information recording medium having the same capacity as a DVD-ROM and having good repetitive recording characteristics in a wide recording linear velocity region, and a sputtering target for manufacturing the same.

The inventors of the present invention have conducted intensive studies to solve the above problems, and as a result, good sensitivity was obtained by using an alloy mainly composed of Sn, Sb, Ga and Ge as a material for forming a recording layer. For example, when a DVD-based recording system having a wavelength of 660 nm and a lens NA of 0.65 is used, sufficient recording sensitivity and good overwriting are performed at a recording speed of about 35 m / s or more. It has been found that it is possible to obtain an information recording medium that can obtain characteristics and storage reliability, and that has the same capacity as a DVD-ROM and excellent repetitive recording characteristics in a wide recording linear velocity region.
That is, the above problems are solved by the following inventions 1) to 12) (hereinafter referred to as inventions 1 to 12).
1) At least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer are formed in this order on a transparent substrate, and information recording is performed by irradiating a laser beam with the crystalline state and non-crystalline state of the phase change recording layer. The alloy, which is formed by a reversible phase change in a crystalline state and is a main component of a material constituting the phase change recording layer, has a composition formula of Sn _α Sb _β Ga _γ Ge _δ [α, β , Γ, and δ are composition ratios (atomic%) of the respective elements, and α + β + γ + δ = 100], and α, β, γ, and δ satisfy the following relationship.
5 ≦ α ≦ 25
40 ≦ β ≦ 91
2 ≦ γ ≦ 20
2 ≦ δ ≦ 20
2) The phase-change information recording medium according to 1), wherein 5 ≦ α ≦ 20, 40 ≦ β ≦ 85, 5 ≦ γ ≦ 20, and 5 ≦ δ ≦ 20.
3) The phase change type information recording medium according to 2), wherein 10 ≦ α ≦ 20, 50 ≦ β ≦ 80, 5 ≦ γ ≦ 15, and 5 ≦ δ ≦ 15.
4) The phase change recording layer according to 1) to 3), wherein the phase change recording layer contains at least one element selected from the group consisting of Ag, Zn, In, and Cu in an amount of 1 to 10 atomic% with respect to the alloy. The phase change type information recording medium according to any one of the above.
5) The phase change type information recording medium according to 1) to 4), wherein the phase change recording layer contains Te in an amount of 1 to 10 atomic% with respect to the alloy.
6) When the thicknesses of the first protective layer, the phase change recording layer, the second protective layer, and the reflective layer are t1 to t4 (nm) and the wavelength of the laser beam is λ (nm), the following relationship is satisfied. The phase change type information recording medium according to any one of 1) to 5), characterized in that:
t1: 0.070 ≦ t1 / λ ≦ 0.160
t2: 0.015 ≦ t2 / λ ≦ 0.032
t3: 0.005 ≦ t3 / λ ≦ 0.040
t4: 0.100 ≦ t4 / λ
7) The phase change type according to any one of 1) to 6), wherein an interface layer made of SiO ₂ having a thickness of ₂ to 10 nm is provided between the phase change recording layer and the first protective layer. Information recording medium.
8) A layer obtained by rotating a phase-change information recording medium having a stack of layers at a constant linear velocity in the range of 10 to 21 m / s and performing initial crystallization at a power density of 15 to 40 mW / μm ^2. The phase change type information recording medium according to any one of 1) to 7), wherein
9) Sn _α Sb _β Ga _γ Ge _δ (provided that 5 ≦ α ≦ 25, 40 ≦ β ≦ 91, 2 ≦ γ ≦ 20, 2 ≦ δ ≦ 20, α, β, γ, and δ are atomic%, α + β + γ + δ = 100) A sputtering target for producing a phase change type information recording medium comprising an alloy having a composition represented by 100).
10) The sputtering target according to 9), wherein 5 ≦ α ≦ 20, 40 ≦ β ≦ 85, 5 ≦ γ ≦ 20, and 5 ≦ δ ≦ 20.
11) The sputtering target according to 10), wherein 10 ≦ α ≦ 20, 50 ≦ β ≦ 80, 5 ≦ γ ≦ 15, and 5 ≦ δ ≦ 15.
12) The alloy according to any one of 9) to 11), wherein the alloy is a main component and at least one element selected from Ag, Zn, In, Cu, and Te is contained in the alloy at 1 to 10 atomic%. The sputtering target for producing a phase change type information recording medium according to any one of the above.

Hereinafter, the present invention will be described in detail.
In the present invention, in order to achieve high linear velocity recording up to 10 times speed, the alloy of the composition formula defined in the present invention 1 is used as a main component of the material constituting the phase change recording layer. Here, the main component means that it accounts for 90 atomic% or more of the entire recording layer material.
Since the Sn ₅₀ Sb ₅₀ compound has a low melting point of 425 ° C. and a very high crystallization rate, it is considered that it has a possibility of realizing a high-speed recording medium with good recording sensitivity. However, the crystallization speed of the Sn ₅₀ Sb ₅₀ compound is higher as it crystallizes at room temperature, and cannot be made amorphous by the current DVD + RW evaluation apparatus. Therefore, the Sn ₅₀ Sb ₅₀ alone is used as the phase change recording layer of the DVD + RW. It is not possible. Therefore, by improving the composition using Sn ₅₀ Sb ₅₀ as a matrix, a material capable of repeating recording and having excellent storage stability was searched.
As a result, by simultaneously adding two kinds of Ga, which have an effect of facilitating crystallization and making it amorphous, and Ge, which has an effect of storage stability, optical recording which can be repeatedly recorded and has excellent storage stability. We found that a medium could be provided. When only Ga is added, the reflectance of the crystal phase decreases after long-term storage, and shelf characteristics (recording / reproduction characteristics after long-term storage), which is one of the evaluation items of storage stability, deteriorates. . When only Ge is added, the amorphous mark length varies, and the jitter characteristics are not improved.

Since Ga and Ge have the effect of reducing the crystallization speed of Sn ₅₀ Sb ₅₀ , the crystallization speed can be changed by adjusting Ga + Ge atomic%. For example, when Ga + Ge = 20 at% or more, the recording characteristics at low speeds are particularly good, and when Ga + Ge = 10 to 15 at%, the high-speed recording characteristics at 8 × speed or more are particularly good.
In the composition formula of the present invention 1, if Sn is less than 5 atomic%, the melting point becomes high and the sensitivity is deteriorated. If Sn is more than 25 atomic%, the crystallization speed becomes too fast to make the film amorphous. Not preferred. On the other hand, if Sb is less than 40 at%, the melting point becomes high and the sensitivity is deteriorated. If Sb exceeds 91 at%, the storage reliability of the amorphous mark is deteriorated, which is not preferable. If the content of Ga and Ge is less than 2 atomic%, the storage reliability deteriorates, and if the content of Ga and Ge exceeds 20 atomic%, the crystallization temperature becomes too high, and the initial crystallization becomes difficult, which is not preferable. When all of the above relational expressions are satisfied, it is possible to obtain an information recording medium which is excellent in storage stability and capable of repeating recording at a recording linear velocity equal to or higher than that of DVD with a recording linear velocity equal to or higher than that of DVD-ROM.

Further, by using the alloy having the composition specified in the second aspect of the present invention, it is possible to obtain an information recording medium which has the same capacity as a DVD-ROM and has a good recording performance at a recording linear velocity of 10 times or more that of a DVD.
Further, by using the alloy having the composition specified in the third aspect of the present invention, it is possible to obtain an information recording medium having good repetitive recording at a linear speed between 3 × and 8 × of DVD. According to the third aspect of the present invention, since repetitive recording is good in a wide recording linear velocity region, information can be recorded on a recording medium by CAV (constant rotation speed method) in which the recording linear velocity differs at a radial position.
Further, at least one element selected from the group consisting of Ag, Zn, In and Cu can be added to the alloy. Thereby, the storage reliability can be further improved. If the addition amount of these elements is less than 1 atomic% with respect to the alloy, there is no effect, and if it exceeds 10 atomic%, the crystallization temperature becomes too high and initial crystallization becomes difficult.
Further, Te can be added to the alloy. By adding 1 to 10 atomic% of Te, initial crystallization is facilitated and a uniform crystal state is easily obtained. As a result, an increase in jitter due to repeated recording from the first time to about 10 times can be reduced.
Furthermore, in the present invention 6, an appropriate thickness range of the first protective layer, the phase change recording layer, the second protective layer and the reflective layer is defined in relation to the laser wavelength λ (nm). Once the wavelength of the laser beam used for recording / reproducing on the phase-change type information recording medium is determined, the medium can be designed by selecting an appropriate film thickness range according to these equations. A preferred wavelength range is λ = 660 ± 10 nm. Details will be described later.
Further, the present inventions 9 to 12 are sputtering targets used for manufacturing the phase change recording layer.

Next, each layer configuration of the phase change type information recording medium of the present invention will be described.
FIG. 1 is a cross-sectional view for explaining one embodiment of the phase change type information recording medium of the present invention. The first protection layer, the phase change recording layer, the second protection layer, and the like are formed on a transparent substrate by, for example, a sputtering method. A reflective layer is formed in this order, and a protective layer made of an ultraviolet (UV) curable resin is formed on the reflective layer by spin coating. If necessary, another substrate may be attached on the protective layer for further reinforcement or protection of the recording medium.
As the transparent substrate, for example, a polycarbonate substrate having a guide groove for tracking on the surface and having a diameter of 12 cm and a thickness of 0.6 mm and having excellent workability and optical characteristics is preferable. The guide groove for tracking is preferably a meandering groove having a pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm, and a groove width of 0.2 to 0.4 μm. In particular, by increasing the depth of the groove, the reflectance of the recording medium decreases, and the degree of modulation can be increased.

The first protective layer is required to have good adhesion to the transparent substrate and the phase change recording layer, high heat resistance, and the like. Further, since the first protective layer also serves as a light interference layer that enables effective light absorption of the phase change recording layer, it is preferable that the first protective layer have optical characteristics suitable for repeated recording at a high linear velocity. . A preferred material is (ZnS) ₈₀ (SiO ₂ ) ₂₀ .
The film thickness t1 (nm) of the first protective layer is suitably 0.070 ≦ t1 / λ ≦ 0.160 as the wavelength λ (nm) of the laser beam. Is lost, and when the thickness is large, interfacial separation easily occurs. As the sputtering conditions, an input power of 3 kW and an Ar gas pressure (atmospheric pressure of the film forming chamber) of 2E-3 Torr (2 × 10 ⁻³ Torr) are exemplified.

The film thickness t2 (nm) of the phase-change recording layer is suitably 0.015 ≦ t2 / λ ≦ 0.032, where λ (nm) is the wavelength of the laser beam. The function as a recording layer may be lost. On the other hand, if the recording layer is thick, the recording sensitivity is deteriorated.
The formation of the recording layer is preferably performed by a sputtering method. As an example of a method for producing a sputtering target, the charged amount is weighed in advance, heated and melted in a glass ampule, then taken out and crushed by a crusher, and the obtained powder is sintered by heating and sintering. Target can be obtained. Examples of the sputtering conditions include an input power of 1 kW and an Ar gas pressure (atmospheric pressure of a film forming chamber) of 2E-3 Torr.

The second protective layer is required to have good adhesion to the phase change recording layer and the reflective layer, high heat resistance, and the like. Further, since the phase change recording layer also plays a role as a light interference layer that enables effective light absorption, it is desirable that the phase change recording layer has optical characteristics suitable for repeated recording at a high linear velocity. Preferred materials include (ZnS) ₈₀ (SiO ₂ ) ₂₀ . The film thickness t3 (nm) of the second protective layer is suitably 0.005 ≦ t3 / λ ≦ 0.040, where λ (nm) is the wavelength. If the thickness is smaller than this range, the recording sensitivity is deteriorated. Is too crowded. As the sputtering conditions, an input power of 3 kW and an Ar gas pressure (pressure in a film forming chamber) of 2E-3 Torr are exemplified.
Ag or Ag-Cu, Ag-Pd, Ag-Ti, or the like having a high thermal conductivity is suitable for the reflective layer. The film thickness t4 (nm) of the reflective layer is suitably 0.100 ≦ t4 / λ, where λ is the wavelength. If the thickness is smaller than this range, the heat radiation effect cannot be obtained. As the sputtering conditions, an input power of 5 kW and an Ar gas pressure (pressure in a film forming chamber) of 2E-3 Torr are exemplified.

Further, a third protective layer may be provided between the second protective layer and the reflective layer. When the second protective layer material contains S (sulfur), this layer has a function of preventing the generation of Ag ₂ S by the reaction between S and Ag contained in the reflective layer. Preferred _{materials, SiC, TiC, TiO 2,} TiC-TiO 2, NbC, include _{NbO 2, NbC-NbO 2,} SiO 2, Ta 2 O 5, Al 2 O 3, ITO or the like.
Further, it is preferable to provide an interface layer made of SiO ₂ between the first protective layer and the phase change recording layer. By providing SiO ₂ as an interface layer with a thickness of ₂ to 10 nm, damage to the substrate when recording with high power can be reduced, so that the repetitive recording characteristics in high power recording become good and the recording power margin is widened. can do. If it is less than 2 nm, it is difficult to form a uniform SiO ₂ film, and if it exceeds 10 nm, film peeling is likely to occur.

The initial crystallization is preferably performed at a power density of 15 to 40 mW / μm ² by rotating the phase change type information recording medium at a constant linear velocity in the range of 10 to 21 m / s. The initial characteristics of the repetitive recording are determined by the conditions of the initial crystallization, but the faster the material is, the faster the initial crystallization is preferably performed. When initial crystallization is performed at a linear velocity of less than 10 m / s, large crystal grains grow, so that the amorphous mark edges are likely to be non-uniform and the jitter characteristics are deteriorated. On the other hand, if the speed exceeds 21 m / s, the followability of the disc deteriorates, and the distribution tends to occur in the reflectance. If the power density is less than 15 mW / μm ² , a uniform crystal cannot be obtained due to insufficient power. If the power density exceeds 40 mW / μm ² , the power is too strong and the repetitive recording characteristics deteriorate.

According to the present invention, the initial crystallization is easy, the recording sensitivity is good even at the same linear capacity as DVD-ROM, and the recording linear velocity is 10 times or more. A phase change type information recording medium having excellent properties and a sputtering target for manufacturing the same can be provided.
Further, it is possible to provide an information recording medium having the same capacity as that of a DVD-ROM and excellent repetitive recording characteristics in a wide recording linear velocity region, and a sputtering target for manufacturing the same.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

(Examples 1 to 8)
An information recording medium (disk) was produced as follows.
On a polycarbonate substrate having a track pitch of 0.74 μm, a groove depth of 27 nm, a diameter of 12 cm and a thickness of 0.6 mm, a first protective layer, a phase-change recording layer, a second protective layer, a third protective layer, and a reflection layer were formed by sputtering. The layers were formed sequentially.
The first protective layer was made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ as a target and had a thickness of 80 nm.
For the phase change recording layer, a sputtering target having a composition (atomic%) corresponding to the material composition shown in Table 1 below was used, and the film thickness was 20 nm.
The thickness of the second protective layer was 14 nm using (ZnS) ₈₀ (SiO ₂ ) ₂₀ as a target.
The third protective layer used a SiC target and had a thickness of 4 nm.
The reflective layer used an Ag target and had a thickness of 180 nm.
Further, an acrylic-based cured resin having a thickness of 5 to 10 μm was applied on the reflective layer by a spinner, and then cured by ultraviolet rays to form an organic protective film.
Further, a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm was bonded thereon using an adhesive, and initial crystallization was performed using a semiconductor laser having a wavelength of 810 nm.
The recording / reproduction was evaluated using a pickup head having a wavelength of 660 nm and an NA of 0.65. The recording linear velocity was 10.5 m / s (corresponding to DVD 3 × speed) and 28 m / s (corresponding to DVD 8 × velocity), and the recording power was changed according to the linear velocity. The bias power was 0.2 mW, and the erase power was 2 to 15 mW, and each was optimized.
For these information media, the measurement result of the C / N ratio when 3T was repeatedly recorded 10 times [measurement of the ratio between the noise (N) level and the signal intensity (C: carrier) using a spectrum analyzer] was performed. It is shown in Table 3. When realizing a rewritable optical disk system, its C / N ratio needs to be at least 45 dB. In the recording media of Examples 1 to 8, the C / N ratio of 45 dB or more was obtained regardless of whether the recording was repeatedly performed at 10.5 m / s, which is equivalent to DVD triple speed, or when the recording was repeatedly performed at 28 m / s, which was equivalent to DVD 8 × speed. I got it.

(Comparative Examples 1 to 7)
An information recording medium (disk) was prepared in the same manner as in Example 1 except that the phase change recording layer was formed using a sputtering target having a composition (atomic%) corresponding to the material composition shown in Table 2 below. Evaluation was performed in the same manner as in Example 1.
The results are shown in Table 4. The C / N ratio when recording was repeatedly performed at 10.5 m / s and 28 m / s was 45 dB or less except for the case of 10.5 m / s in Comparative Example 1.

(Examples 9 to 15)
An information recording medium (disk) was produced as follows.
On a polycarbonate substrate having a track pitch of 0.74 μm, a groove depth of 27 nm, a diameter of 12 cm and a thickness of 0.6 mm, a first protective layer, a phase-change recording layer, a second protective layer, a third protective layer, and a reflection layer were formed by sputtering. The layers were formed sequentially.
The first protective layer used was (ZnS) ₈₀ (SiO ₂ ) ₂₀ as a target, and had a thickness of 70 nm.
For the phase change recording layer, a sputtering target having a composition (atomic%) corresponding to the material composition shown in Table 5 below was used, and the film thickness was 18 nm.
The second protective layer used was (ZnS) ₈₀ (SiO ₂ ) ₂₀ as a target, and had a thickness of 10 nm.
The third protective layer used a SiC target and had a thickness of 4 nm.
The reflective layer used an Ag target and had a thickness of 140 nm.
Further, an acrylic-based cured resin having a thickness of 5 to 10 μm was applied on the reflective layer by a spinner, and then cured by ultraviolet rays to form an organic protective film.
Further, a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm was bonded thereon using an adhesive sheet, and the initial crystallization was performed using a semiconductor laser having a wavelength of 810 nm.
The recording / reproduction was evaluated using a pickup head having a wavelength of 660 nm and an NA of 0.65. The recording linear velocity was 17.5, 24.5, 35.0 m / s, and the recording power was changed according to the linear velocity. The bias power was 0.2 mW, and the erase power was 2 to 15 mW, and each was optimized. Each recording strategy was optimized. All reproduction was performed at a linear velocity of 3.5 m / s and a power of 0.7 mW.
Table 6 shows the results of each evaluation.
Jitter is a value obtained by normalizing data to clock jitter σ with the detection window width Tw.
The storage stability was determined by writing a recording mark on the sample and holding the sample in a thermostat at 80 ° C. and 85% RH for 300 hours. A case of 3% or more was evaluated as x.
The stability of the reproduction light was evaluated by writing a recording mark on the sample and irradiating the sample with the reproduction light at a linear velocity of 3.5 m / s and a power of 1.0 mW for 10 minutes. A case of not less than 3% and a case of 3% or more were evaluated as x.
Initial crystallization of the phase change type information recording media of Examples 9 to 15 could be easily performed, and the reflectance was uniform in the circumference. The melting point is between 400 and 600 ° C., and at recording linear velocities of 17.5, 24.5, and 35.0 m / s, the jitter shows 10% or less even after 1000 overwrites, and the recording sensitivity is good. As a result, a medium having good storage stability was obtained. Further, the modulation degree of each sample showed 60% or more even after 1000 times of overwriting, and there was almost no change even after the storage stability test. In particular, the recording media of Examples 12 and 13 showed no change even after being kept in a thermostat at 80 ° C. and 85% RH for 600 hours. The reflectance showed 20% or more after 1000 overwrites, and there was almost no change after the storage stability test.

(Comparative Example 8)
An information recording medium (disk) was produced in the same manner as in Example 9, except that the phase change recording layer material was changed to Ag ₃ In ₄ Sb ₇₅ Te ₁₈ , and evaluation was conducted in the same manner as in Example 9.
The composition of the recording layer material is shown in Table 5, and the evaluation results are shown in Table 6. At each recording linear velocity, higher recording power was required than in Examples 9 to 15. At a linear velocity of 35.0 m / s, the initial jitter was as high as 13.4% and the modulation was as low as 50% even when writing was performed at 38 mW which is the limit of the LD used. When the linear velocities were 17.5 and 24.5 m / s, the storage stability was good, but when the linear velocity was 35.0 m / s, the amorphous marks were not sufficiently formed, so that the deterioration was considered to be fast. .

(Comparative Example 9)
An information recording medium (disk) was prepared in the same manner as in Example 9 except that the phase change recording layer material was changed to Ge ₅ Ga ₄ Sb ₈₀ Te ₁₁ , and evaluation was performed in the same manner as in Example 9.
The composition of the recording layer material is shown in Table 5, and the evaluation results are shown in Table 6. When the recording linear velocity is 17.5 m / s, the jitter is 10% or less up to 100 times of overwriting. .3%. As for the storage stability, the rise in jitter was less than 3%. The reflectance was 23% before the storage test, but decreased to 16% after the storage test, and there was a problem in storage stability. The reproduction light stability was good. When the recording linear velocity is 35.0 m / s, the initial jitter is as high as 18.8%. However, since the crystallization speed is low, it is considered that sufficient mark writing could not be performed at this linear velocity.

(Example 16)
On a polycarbonate substrate having a track pitch of 0.74 μm, a groove depth of 27 nm, a diameter of 12 cm and a thickness of 0.6 mm, a first protective layer, a phase-change recording layer, a second protective layer, a third protective layer, and a reflection layer were formed by sputtering. The layers were formed sequentially.
The first protective layer was made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ as a target and had a thickness of 60 nm.
For the phase change recording layer, a sputtering target of Sn ₁₈ Sb ₆₉ Ga ₆ Ge ₇ was used, and the film thickness was 16 nm.
The thickness of the second protective layer was 8 nm using (ZnS) ₈₀ (SiO ₂ ) ₂₀ as a target.
The third protective layer used a SiC target and had a thickness of 4 nm.
The reflective layer used an Ag target and had a thickness of 140 nm.
Further, an acrylic-based cured resin having a thickness of 5 to 10 μm was applied on the reflective layer by a spinner, and then cured by ultraviolet rays to form an organic protective film.
Further, a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm was bonded thereon using an adhesive.
The recording medium is rotated at a constant linear velocity of 20 m / s and irradiated with a laser beam having a power density of 25 mW / μm _{2 in} the radial direction while moving at a rate of 50 μm / r using an optical head having a beam width of 75 μm. Crystallization was performed.
The recording / reproduction was evaluated using a pickup head having a wavelength of 660 nm and an NA of 0.65. The recording linear speed was 10.5 m / s (3 times speed), 14 m / s (4 times speed), 21 m / s (6 times speed), and 28 m / s (8 times speed), and the recording power was changed according to the linear speed. The bias power was 0.2 mW, and the erase power was 5 to 10 mW, and each was optimized.
FIG. 2 shows the jitter from the first time to 1000 repetitive recordings. The jitter was 10% or less at all recording linear velocities. In order to realize a rewritable optical disk system, at least a jitter of 10% or less is required.

(Example 17)
An information recording medium (disk) was produced in the same manner as in Example 16 except that the material of the phase change recording layer was changed to Ga ₆ Sb ₆₇ Sn ₁₈ Ge ₆ Te ₃ .
The information recording medium is rotated at a constant linear velocity of 15 m / s, and irradiated with a laser beam having a power density of 20 mW / μm ^{2 in} a radial direction while moving at 50 μm / r using an optical head having a beam width of 75 μm. Initial crystallization was performed. When the same evaluation as in Example 16 was performed, as shown in FIG. 3, the jitter particularly from the first time to the tenth repetitive recording was good, and was within 9%, which is the standard value of DVD.

(Example 18)
The information recording medium of Example 16 was manufactured by providing an interface layer made of SiO ₂ at a thickness of 2 nm between the first protective layer and the phase change recording layer. This information recording medium and the information recording medium of Example 16 were rotated at a constant linear velocity of 20 m / s, and a laser beam having a power density of 25 mW / μm ² was fed in the radial direction using an optical head having a beam width of 75 μm to 50 μm / r. Initial crystallization was performed by irradiating while moving. The repetitive recording characteristics when the recording linear velocity was 28 m / s (corresponding to 8 times speed) and the recording power was 28, 30, 32, 34, 36 and 38 mW were evaluated.
The result in the case of Example 16 is shown in FIG. 4, and the result in the case of Example 18 is shown in FIG. In both Examples 16 and 18, the jitter was within 9% at the optimum power. In particular, in Example 18, the jitter at the 1000th repetitive recording was within 9% even at a high power of 36 mW or more. By providing the SiO ₂ interface layer, the repetitive recording characteristics in high power recording were improved, and the recording power margin could be widened.

FIG. 1 is a cross-sectional view illustrating one embodiment of a phase change type information recording medium of the present invention. FIG. 21 is a diagram showing jitter from the first time to 1000 times of repetitive recording of the information recording medium of Example 16. FIG. 21 is a diagram showing jitter from the first time to 1000 times of repetitive recording of the information recording medium of Example 17; FIG. 22 is a diagram showing repetitive recording characteristics of the information recording medium of Example 16. 28 is a diagram showing the repetitive recording characteristics of the information recording medium of Example 18. FIG.

Claims (12)

On a transparent substrate, at least a first protective layer, a phase change recording layer, a second protective layer, and a reflective layer are formed in this order, and information recording is performed by irradiating a laser beam with a crystalline state and an amorphous state of the phase change recording layer. The alloy, which is formed by the reversible phase change of the state and is the main component of the material constituting the phase change recording layer, has a composition formula of Sn _α Sb _β Ga _γ Ge _δ [α, β, γ , Δ is the composition ratio (atomic%) of each element, α + β + γ + δ = 100], and α, β, γ, and δ satisfy the following relationship.
5 ≦ α ≦ 25
40 ≦ β ≦ 91
2 ≦ γ ≦ 20
2 ≦ δ ≦ 20   2. The phase change type information recording medium according to claim 1, wherein 5 ≦ α ≦ 20, 40 ≦ β ≦ 85, 5 ≦ γ ≦ 20, 5 ≦ δ ≦ 20.   3. The phase change type information recording medium according to claim 2, wherein 10 ≦ α ≦ 20, 50 ≦ β ≦ 80, 5 ≦ γ ≦ 15, 5 ≦ δ ≦ 15.   The phase change recording layer contains at least one element selected from the group consisting of Ag, Zn, In and Cu in an amount of 1 to 10 atomic% with respect to the alloy. 3. The phase-change information recording medium according to claim 1.   The phase change type information recording medium according to claim 1, wherein the phase change recording layer contains Te in an amount of 1 to 10 atomic% with respect to the alloy. When the thicknesses of the first protective layer, the phase change recording layer, the second protective layer, and the reflective layer are t1 to t4 (nm) and the wavelength of the laser beam is λ (nm), the following relationship is satisfied. The phase change type information recording medium according to any one of claims 1 to 5, wherein
t1: 0.070 ≦ t1 / λ ≦ 0.160
t2: 0.015 ≦ t2 / λ ≦ 0.032
t3: 0.005 ≦ t3 / λ ≦ 0.040
t4: 0.100 ≦ t4 / λ 7. The phase change type information recording according to claim 1, further comprising an interface layer made of SiO2 having a thickness of ₂ to 10 nm between the phase change recording layer and the first protective layer. Medium. It is obtained by rotating a phase-change information recording medium in which each layer is laminated at a constant linear velocity in a range of 10 to 21 m / s and performing initial crystallization at a power density of 15 to 40 mW / μm ^2. The phase change type information recording medium according to claim 1, wherein: Sn _α Sb _β Ga _γ Ge _δ (provided that 5 ≦ α ≦ 25, 40 ≦ β ≦ 91, 2 ≦ γ ≦ 20, 2 ≦ δ ≦ 20, α, β, γ and δ are atomic%, α + β + γ + δ = 100) A sputtering target for producing a phase change type information recording medium comprising an alloy having a composition represented by the formula:   The sputtering target according to claim 9, wherein 5 ≦ α ≦ 20, 40 ≦ β ≦ 85, 5 ≦ γ ≦ 20, and 5 ≦ δ ≦ 20.   The sputtering target according to claim 10, wherein 10 ≦ α ≦ 20, 50 ≦ β ≦ 80, 5 ≦ γ ≦ 15, and 5 ≦ δ ≦ 15. The alloy according to claim 9, wherein at least one element selected from Ag, Zn, In, Cu, and Te is contained in the alloy in an amount of 1 to 10 atomic%. The sputtering target for producing a phase change type information recording medium according to the above item.

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